We do tend to make things sound more difficult than they need to be. Bike commuting doesn't have to be more difficult than "get on bike, ride to work, get off bike". For a 4 mile commuter on an occasional day (that likely you can plan around weather), the bike you have plus an appropriate sized bag to carry what you want would do it to start. I started with a 30 year old Schwinn that I paid $25 for and put $150 into, so I feel your pain. Used that for 4 years, before buying my Trek 7.2, which by that time I knew exactly what I wanted.